Battery Help

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MG MGB and MGB GT Tech Talk

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Nov 29, 2009 14:32:21
rkirk304

I have been using the GT lately, but as it was a nice day, decided to take the roadster out.
No power, so I jumped it and it ran fine. As soon as I turned it off....no power; no start
I jumped it again and put it away.
Could it be anything other than the battery?
Do i need a new one, and if so, which is best?
R

Nov 29, 2009 14:59:31
pooch2

Depends how long you ran it and if it is chargng.

A short run will do nothing for a dead battery.





Nov 29, 2009 15:03:53
Steve S

Put a charger on the battery until full, then see how it goes. It's probably just drained.

Nov 29, 2009 15:18:58
blkcloud

Check the fluid level and top up with distilled water. Then give it a slow overnight charge maybe 2 amps. If you have a battery load tester, or can borrow one, that will tell you where the battery is, life-wise....

Nov 29, 2009 15:22:39
rkirk304

Thanks much.
I will put it on a charger and see.
I drove for about 30 minutes and everything was fine. I then turned it off and it was dead as a dodo!

Nov 29, 2009 15:26:13
James74

The should Be a stamp on the side of the battery with numbers on it. It gives the month and year of the batteries manufacture date. if the battery is over three years old it might be time for a new one.

Nov 29, 2009 15:48:45
Tall Man

Quote: "
The should Be a stamp on the side of the battery with numbers on it. It gives the month and year of the batteries manufacture date. if the battery is over three years old it might be time for a new one."


Alternately, there could be a label with a letter/number date code.

Here's a pic of my B's battery, which needs replaced. The label indicates that it was manufactured in August 2004.

Nov 30, 2009 13:47:52
tomkatb

Robin

This is a fun game with this car. We have all played it several times if we have owned one more that 20 years.

As Steve said charge the battery. But, first check the cells and top up with distilled water.

Then take all the terminals off the battery/s. Clean the connectors and the posts with the cheapo battery terminal cleaner brush from the local discount auto store.

Then put it back together. Wiggle the wire terminals a lot to be sure they are tight. They can be damaged under the bolt/bracket that holds the wire to the terminal.

See if the battery has a date on it. Anything over 5 years old is suspect. Charge the battery overnight.

Take a voltage reading anywhere handy and start the car. Then check the voltage with the car running.
Check the battery voltage the next day.

I bet on dirty battery terminals.

26R is the Autozone Duralast battery for positive ground cars. 26 size for negative ground. I do not think this is your problem.

Nov 30, 2009 16:32:26
obertRo

Robin:

When having drained battery problems, it's nice to know for sure your charging system is not at fault. One easy way to check your charging system is to disconnect the battery while the car is running (pull off a terminal clamp right after jumping the car to life). If it quits, your charging system is at fault.

Good luck.

Robert

Nov 30, 2009 17:00:59
mgacarnut

[

quote=tomkatb]
Robin


26R is the Autozone Duralast battery for positive ground cars. 26 size for negative ground. I do not think this is your problem.[/quote]

Why different batteries for positive versus negative ground cars? Location of the terminals?

Nov 30, 2009 18:29:58
lars49

Quote: "


One easy way to check your charging system is to disconnect the battery while the car is running (pull off a terminal clamp right after jumping the car to life).
"


Don't do it, it's a good way to blow the alternator. It is possible to get voltage spikes in excess of 80 volts with the battery disconnected. Those spikes can blow the diodes in the alternator.

Nov 30, 2009 19:24:52
tomkatb

Yes. 26/26R 12 volt.

However in my old car it would have worked with either one. My cables are sort of long.



I do not think your issue is battery. Running fine but, not starting is common. Do the lights work? Often with dirty cables the lights will work but the starter will not. Not always. The routine i described takes 15 minute to treat the terminals and then overnight on the charger then you will know for sure.

Is the battery old. Mine typically last 7+ years.

Nov 30, 2009 20:55:28
MimosaB

Ditto the above, but I don't know about pulling off a terminal when the car is running. If its one thing I have found about my B that at time frustrates me, its the battery. The terminals have to be cleaned regularly, and checking the cables for corrosion is a good idea as well. Trickle charging the battery with the caps off and cells filled overnight is the way to go. Be careful about overtightening the clamps, as doing so cracked the case on my old 6 volt battery. Wound up going with a Die-Hard 12V and have not looked back since. Also, while your at it remember the connections to the starter. The leads there can be loose and cause a no start when all else checks out. Sound battery maintenance is one of my pet peeves with this car, especially since it is driven so little.

Nov 30, 2009 21:10:32
Frank 79 Roadster

one word........BatteryMinder......thebatteryminder.com.........get one.

Nov 30, 2009 21:29:58
pooch2

Quote: "
[quote=obertRo]


One easy way to check your charging system is to disconnect the battery while the car is running (pull off a terminal clamp right after jumping the car to life).
"


Don't do it, it's a good way to blow the alternator. It is possible to get voltage spikes in excess of 80 volts with the battery disconnected. Those spikes can blow the diodes in the alternator.[/quote]

Did you know that when the reference voltage stops to the field windings, the alternator can spike over 100 volts.

Hope your heart is in good nick.

Nov 30, 2009 22:27:03
ingoldsb

Quote: "
When having drained battery problems, it's nice to know for sure your charging system is not at fault. One easy way to check your charging system is to disconnect the battery while the car is running (pull off a terminal clamp right after jumping the car to life). If it quits, your charging system is at fault.
"


Double don't do that - as several people have said - it may spike.

BUT besides that - more often than not the engine will keep running (if the alternator doesn't get fried). Probably won't work on a modern computer controlled car, but an older car won't notice the pulsating DC (which the battery smooths out).

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